The use of MIMO (Multiple Input Multiple Output) refers in the wireless-communication field to employing a plurality of antennas or, as the case may be, transmitting nodes for transmitting data and employing a plurality of antennas or, as the case may be, receiving nodes for receiving data. Said antennas or nodes therein form in each case an antennas array. The antenna array on the sending side is referred to as a transmitting-antenna array and the antenna array on the receiving side as a receiving-antenna array. This kind of signal transmission is used in a wireless communication system to exploit multi-path propagating and thereby limit the impact of signal fading. The term “cooperative MIMO” is used when a plurality of autonomous instances or, as the case may be, nodes form an antenna array for transmitting or, as the case may be, receiving data or, as the case may be, messages. With cooperative MIMO, each antenna is formed by an autonomous node, for example a sensor node, in contrast to antenna arrays that are configured to form a single instance.
In the case of cooperative MIMO, a plurality of instances or transmitting nodes that have received a message from a transmitter unit, emit said data to a receiving-antenna array. Said receiving-antenna array likewise contains a plurality of nodes that receive the transmitted data and deliver it to a receiver unit which constructs the originally transmitted message therefrom.
With the cooperative MIMO method it is possible to employ different techniques for transmitting data from the transmitting-antenna array to the receiving-antenna array with a low error rate.
It possible for the instances or transmitting nodes of the transmitting-antenna array to emit the same data. The receiving nodes of the receiving-antenna array in each case construct, as far as possible, the originally used data from the received data or attempt to reestablish it by means of, for example, a rake filter. Said reconstructed data is conveyed by the receiving-antenna array's receiving nodes to the actual receiver unit, which reconstructs the original message through, for example, a majority decision. That procedure can be referred to also as a widely practiced MISO (Multiple Input Single Output) method.
The transmitting nodes or, as the case may be, instances of the transmitting-antenna array can alternatively in each case emit different data, with said data being the result of a special encoding of the output data or, as the case may be, of the original message originating from the transmitter unit. The data received by the instances or, as the case may be, receiving nodes of the receiving-antenna array constitutes a mixture of the transmitted data. Said data is forwarded by the receiving-antenna array's receiving nodes to the receiver unit, which then reconstructs the original message from the received data of all receiving nodes. With that procedure the individual instances or, as the case may be, receiving nodes of the receiving-antenna array cannot perform reconstructing of the data originally sent.
Another known transmission technique is what is termed the MISO method. With MISO (Multiple Input Single Output), as with the above-described MIMO method a plurality of antennas are used for transmitting a message. However, only one antenna is employed for receiving in the case of MISO.
With conventional, cooperative MIMO transmission techniques the instances or, as the case may be, transmitting nodes of the transmitting-antenna array convey data without first checking whether it originates from an authorized transmitter unit. The instances or, as the case may be, receiving nodes of the receiving-antenna array also forward the received data unchecked to the message's indicated receiver unit. Thus neither on the receiving side nor on the sending side does any authenticating of the data's sender take place. With this conventional procedure the data obtained therefore has to be processed in order to reconstruct the originally sent message and then authenticate the message's sender on the basis of the reconstructed message. Thus the sender of the message will not be authenticated until the message has been reconstructed on the receiving side.
Attackers can exploit this procedure to smuggle in data packets or messages unnoticed. It is also possible for attackers to unnecessarily load the intermediate nodes or, as the case may be, receiving nodes as well as the receiver, for example to increase the computing effort required on the receiving side. That undesired loading on the receiving side can result in undesired exploiting of communication resources from the receiving side, for example in increased power consumption by the participating nodes. The lifespan can thereby be shortened by the attacker in the case particularly of battery-operated nodes, for example receiving nodes of the receiving-antenna array. So with the conventional procedure for transmitting data an attacker can not only carry out a denial-of-service attack but also cause his or her own data to be forwarded.